Computer Networks - Quizzes

Front 1

What is the difference between a host and an end system? List the types of end systems. Is a Web server an end system?

Back 1

There is no difference. Throughout this course, the words “host” and “end system” are used interchangeably. End systems include PCs, workstations, Web servers, mail servers, Internet-connected PDAs, WebTVs, etc.

Front 2

What are the two types of services that the Internet provides to its applications?

Back 2

The Internet provides its applications a connection-oriented service (TCP) and a connectionless service (UDP). Each Internet application makes use of one these two services.

Front 3

Does a grid and metacomputing systems mean the same? Justify your answer.

Back 3

A grid is a computing infrastructure that is analogous to a processor while a grid with network operating system is a metacomputer that looks to the user as a single computer.

Front 4

List basic three types of grids?

Back 4

Compute, data and access grids

Front 5

a. Is the wired Internet larger than a wireless one? How many times larger? b. Is Wi-Fi and IEEE 802.11 generally the same concepts?

Back 5

a. Yes, three times b. Yes

Front 6

Differentiate P2P vs. S2S?

Back 6

In P2P peers are in generally computing devices with the same communication protocols, in S2S peers are rather SW components with the same interfaces.

Front 7

Is a Web-based system a client-server system? Why?

Back 7

Yes. A Web browser is a client that requests a service from an HTTP server. Thus, the Web server provides usually HTML/XML documents over HTTP to its clients.

Front 8

What is defined by network protocols? a. format b. order of msgs sent c. order of msgs received d. actions taken on msg transmission, receipt e. transmission speed f.. link physical media g. all the above

Back 8

a,b,c, and d

Front 9

What are some of the physical media that network can run over?

Back 9

For example: twisted pair, coax, optical fiber, radio.

Front 10

What is the basic protocol of Web-based systems?

Back 10

HTTP: Hypertext Transfer Protocol

Front 11

List at least 3 of 8 fallacies of distributed computing?

Back 11

1. The network is reliable 2. Latency is zero 3. Bandwidth is infinite 4. The network is secure 5. Topology doesn't change 6. There is one administrator 7. Transport cost is zero 8. The network is homogeneous

Front 12

Explain the main difference between a program and metaprogram?

Back 12

Instructions of a program (CPU instructions) are executed on the same host while instructions of metaprogram (in fact programs) execute on multiple hosts (grid).

Front 13

SOA consists of: a. service requestor b. service provider c. service proxy d. service registry e. client f. server g. all the above

Back 13

a, b, and d

Front 14

What are the two types of definitions of the Internet?

Back 14

1. nut and bolts-edge, core, and links 2. service-oriented: connection-oriented and connectionless services for distributed applications

Front 15

What information is used by a process running on one host to identify a process running on another host?

Back 15

The IP address of the destination hosts and the port number of the destination socket.

Front 16

Suppose host A is sending a large file to host B over a TCP connection. If the sequence number for a segment of this connection is m, then the segment number for the subsequent segment will necessarily be m + 1.

Back 16

false

Front 17

Suppose host A sends two TCP segments back to back to host B over a TCP connection. The first segment has sequence number 90; the second has sequence number 110.
a. How much data is in the first segment?
b. Suppose that the first segment is lost but the second segment arrives at B. In the acknowledgment that host B sends to host A, what will be the acknowledgment number?

Back 17

a. 20 bytes b. ack number=90

Front 18

True or false? Consider congestion control in TCP. When the time expires at the sender, the threshold is set to one half of its previous value.

Back 18

False, it is set to half of the current value of the congestion window.

Front 19

True or false?
a. Suppose host A sends over a TCP connection to host B one segment with sequence number 38 and 4 bytes of data. In the same segment the acknowledgment number is necessarily 42.
b. The TCP segment has a field in its header for RcvWindow?

Back 19

a. false b. true

Front 20

What are the two most important network-layer functions in a datagram network? What are three important network layer functions in a circuit switched network?

Back 20

Datagram-based network layer: forwarding; routing. Additional function of VC-based network layer: call setup.

Front 21

What is the difference between routing and forwarding?

Back 21

Forwarding is about moving a packet from a router’s input link to the appropriate output link. Routing is about determining the end-to-routes between sources and destinations.

Front 22

Do routers have IP addresses? If so, how many?

Back 22

Yes. They have one address for each interface.

Front 23

What is meant by interactivity for streaming stored audio/video? What is meant by interactivity for real-time interactive audio/video?

Back 23

Streaming stored audio/video: pause/resume, re-positioning, fast-forward; real-time interactive audio and video: people communicating and responding in real time.

Front 24

What is the difference between end-to-end delay and packet jitter? What are the causes of packet jitter?

Back 24

End-to-end delay is the time it takes a packet to travel across the network from source to destination. Delay jitter is the fluctuation of end-to-end delay from packet to the next packet.

Front 25

Three types of switching fabrics are distinguished. List and briefly describe each type.

Back 25

Switching via memory; switching via a bus; switching via an interconnection network

Front 26

What is HOL blocking? Does it occur in inputs or output ports?

Back 26

HOL blocking – a queued packet in an input queue must wait for transfer through the fabric because it is blocked by another packet at the head of the line. It occurs at the input port.

Front 27

What is the major function of the network access layer?

Back 27

The network access layer is concerned with the exchange of data between a computer and the network to which it is attached.

Front 28

What is a protocol?

Back 28

A protocol is the set of rules or conventions governing the way in which two entities cooperate to exchange data.

Front 29

What is an application-layer message? A transport-layer segment? A network layer datagram? A link layer frame??

Back 29

Application-layer message: data which an application wants to send and passed onto the transport layer; transport-layer segment: generated by the transport layer and encapsulates application-layer message with transport layer header; network-layer datagram: encapsulates transport-layer segment with a network-layer header; link layer frame: encapsulates network-layer datagram with a link-layer header.

Front 30

What is a protocol architecture?

Back 30

The software structure that implements the communications function. Typically, the protocol architecture consists of a layered set of protocols, with one or more protocols at each layer.

Front 31

What is TCP/IP?

Back 31

Transmission Control Protocol/Internet Protocol (TCP/IP) are two protocols originally designed to provide low level support for internetworking. The term is also used generically to refer to a more comprehensive collection of protocols developed by the Internet community.

Front 32

What is a router?.

Back 32

A router is a device that operates at the Network layer of the Internet (or OSI) model to connect dissimilar networks.

Front 33

Differentiate between guided media and unguided media?

Back 33

With guided media, the electromagnetic waves are guided along an enclosed physical path whereas unguided media provide a means for transmitting electromagnetic waves but do not guide them.

Front 34

What is relationship between a signal’s spectrum and it’s bandwidth.

Back 34

The spectrum of a signal is the frequencies it contains while the bandwidth of a signal is the width of the spectrum.

Front 35

What is the key distinguishing difference between a tier-1 ISP and a tier-2 ISP?

Back 35

A tier-1 ISP connects to all other tier-1 ISPs; a tier-2 ISP connects to only a few of the tier-1 ISPs. Also, a tier-2 ISP is a customer of one or more tier-1 and a tier-1 has an international scope while tier-2 rather national one.

Front 36

What function a modem perform?

Back 36

A modem converts digital information into an analog signal, and conversely.

Front 37

What is QAM?

Back 37

QAM takes advantage of the fact that it is possible to send two different signals simultaneously on the same carrier frequency, by using two copies of the carrier frequency, one shifted by 90° with respect to the other. For QAM, each carrier is ASK modulated.

Front 38

List six access technologies. Classify each one as residential access, company access, or mobile access?

Back 38

1. Dial-up modem over telephone line: residential; 2. DSL over telephone line: residential or small office; 3. Cable to HFC: residential; 4. 100 Mbps switched Etherent: company; 5. Wireless LAN: mobile; 6. Cellular mobile access

Front 39

Is HFC transmission rate dedicated or shared among users? Are collisions possible in a downstream HFC stream?

Back 39

HFC bandwidth is shared among the users. On the downstream channel, all packets emanate from a single source, namely, the head end. Thus, there are no collisions in the downstream channel.

Front 40

Describe the most popular wireless Internet access technologies today. Compare and contrast them?

Back 40

There are two most popular wireless Internet access technologies today: a) Wireless LAN In a wireless LAN, wireless users transmit/receive packets to/from a base station (wireless access point) within a radius of few tens of meters. The base station is typically connected to the wired Internet and thus serves to connect wireless users to the wired network. b) Wide-area wireless access network In these systems, packets are transmitted over the same wireless infrastructure used for cellular telephony, with the base station thus being managed by a telecommunications provider. This provides wireless access to users within a radius of tens of kilometers of the base station.

Front 41

What advantage does a circuit-switched network have over packet-switched network? What advantages does TDM have over FDM in a circuit switched network?

Back 41

A circuit-switched network can guarantee a certain amount of end-to-end bandwidth for the duration of a call. Most packet-switched networks today (including the Internet) cannot make any end-to-end guarantees for bandwidth.
More time slots can be used in a revolving frame than bands in an FDM spectrum that is physically limited. Also in TDM a time slot can hierarchically can be replaced by an inner revolving frame.

Front 42

What is the difference between an internet and grid?

Back 42

An internet is a network of networks that and grid is a collection of virtual services.

Front 43

List five nonproprietary Internet applications and the application layers protocols that they use.

Back 43

The Web: HTTP; file transfer: FTP; remote login: Telnet; Network News: NNTP; e-mail: SMTP.

Front 44

Which layers in the Internet protocol stack does a router process? Which layers does a link-layer switch protocol? Which layers does a does a host process?

Back 44

Routers process layers 1 through 3. (This is a little bit of a white lie, as modern routers sometimes act as firewalls or caching components, and process layer four as well.) Link layer switches process layers 1 through 2. Hosts process all five layers.

Front 45

Consider an application that transmits data at a steady rate (for example, the sender generates an N-bit of data every k-times units, where k is small and fixed). Also, when such an application starts, it will continue running for a relatively long period of time. Answer the following questions, briefly justifying your answer: a. Would a packet-switched network or a circuit-switched network be more appropriate for this application? Why? b. Suppose that a packet-switched network is used and the only traffic in this network comes from such application as described above. Furthermore, assume that the sum of the application data rates is less than the capacities of each and every link. Is some form of congestion control needed? Why?

Back 45

a) A circuit-switched network would be well suited to the application described, because the application involves long sessions with predictable smooth bandwidth requirements. Since the transmission rate is known and not bursty, bandwidth can be reserved for each application session circuit with no significant waste. In addition, we need not worry greatly about the overhead costs of setting up and tearing down a circuit connection, which are amortized over the lengthy duration of a typical application session. b) Given such generous link capacities, the network needs no congestion control mechanism. In the worst (most potentially congested) case, all the applications simultaneously transmit over one or more particular network links. However, since each link offers sufficient bandwidth to handle the sum of all of the applications' data rates, no congestion (very little queueing) will occur.

Front 46

True or false? a. When a user requests a Web page that consists of some text and two images. For this page the client will send one request message and receive three response messages. b. Two distinct Web pages (for example, www.cs.ttu.edu/research.html and www.cs.ttu.edu/students.html ) can be sent over the same persistent connection. c. With nonpersistent connection between browser and origin server, it is possible for a single TCP segment to carry two distinct HTTP request messages. d. The Date: header in the H

Back 46

a) F b) T c) F d) F

Front 47

Consider an HTTP client that wants to retrieve a Web document at a given URL. The IP address of the HTTP server is initially unknown. The Web document at the URL has one embedded GIF image that resides at the same server as the original document. What transport and application-layer protocols besides HTTP are needed in this session?

Back 47

Application layer protocols: DNS and HTTP Transport layer protocols: UDP for DNS; TCP for HTTP

Front 48

Suppose within your Web browser you click on a link to obtain a Web page. Suppose that the IP address for the associated URL is not cached in your local host, so that a DNS lookup is necessary to obtain the IP address. Suppose that n DNS servers are visited before your host receives the IP address from DNS; the successive visits incur an RTT of RTT1, … , RTTn. Further suppose that the Web page associated with the link contains exactly one object, a small amount of HTML text. Let RTT0 denote the RTT between the local host and the server containing the object. Assuming zero transmission time of the object, how much time elapses from when the client clicks on the link until the client receives the object?

Back 48

The total amount of time to get the IP address is RTT1+RTT2+...+RTTn
Once the IP address is known, elapses to set up the TCP connection and another elapses to request and receive the small object. The total response time is 2RTT0+RTT1+RTT2+...+RTTn

Front 49

Two HTTP request methods are GET and POST. Are there any other methods in HTTP/1.0? If so, what are they used for? How about HTTP/1.1?

Back 49

HTTP/1.0: GET, POST, HEAD. HTTP/1.1: GET, POST, HEAD, OPTIONS, PUT, DELETE, TRACE, CONNECT.

Front 50

Is it possible for an application to enjoy reliable data transfer even when the application runs over UDP? If so how?

Back 50

Yes. The application developer can put reliable data transfer into the application layer protocol. This would require a significant amount of work and debugging, however.

Front 51

Explain the difference between TCP Tahoe and TCP Reno.

Back 51

TCP Tahoe unconditionally cuts its congestion widow to 1 MSS and enters a slow-start phase after either type of loss event. TCP Reno cancels the slow-start phase after a triple duplicate ACK.

Front 52

Why is a packet that is received after its scheduled playout time considered lost?

Back 52

A packet that arrives after its scheduled play out time can not be played out. Therefore, from the perspective of the application, the packet has been lost.

Front 53

What is the main difference between RTSP and RTP?

Back 53

RTSP allows a media player to control the transmission of a media stream. RTP can be used for transporting common formats such as PCM, GSM, and MP# for sound and MPEG and H.263.

Front 54

How are different RTP streams in different sessions identified by a receiver? How are different streams from within the same session identified? How are RTP and RTPC packets (as part of the same session) distinguished?

Back 54

RTP streams in different sessions: different multicast addresses; RTP streams in the same session: SSRC field; RTP packets are distinguished from RTCP packets by using distinct port numbers.

Front 55

What is a role of SIP registrar? How is the role of an SIP registrar different from the DNS authoritative server?

Back 55

The role of a SIP registrar is to keep track of the users and their corresponding IP addresses which they are currently using. Each SIP registrar keeps track of the users
that belong to its domain. It also forwards INVITE messages (for users in its domain) to the IP address which the user is currently using. In this regard, its role is similar to that of an authoritative name server in DNS.

Front 56

What is the 32-bit equivalent of the IP address 223.1.3.27?

Back 56

11011111 00000001 00000011 00011100

Front 57

Compare and contrast the IPV4 and IPv6 header fields. Do they have any fields in common?

Back 57

New: expended addressing capabilities-from 32 to 128 bits, a streamlined 40-byte header, flow label and priority. No: fragmentation/reassembly, header checksum, options. Common: version, next header, hop limit (TTL), source and destination addresses but at different length (32 vs. 128 bit).